- REACTIONS OF CARBENES WITH ANIONS
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CHBrCl2, CHCl2I and CHBr2I are prepared by a simple method based on the reaction of dichloro or dibromocarbene with the corresponding alkali metal halogenides under phase transfer conditions.
- Suelzle, Detlev
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- PROCESS FOR PREPARING BROMOTRICHLOROMETHANE
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The present invention relates to a process for preparing bromotrichloromethane comprising a) providing bromine in chloroform; and b) radiation of the resulting solution with light in the range of 350 to 550 nm, wherein said solution of bromine in chloroform is not radiated with radiation of a wavelength below 350nm.
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Page/Page column 6-7
(2018/10/19)
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- Effects of bromide on the formation of THMs and HAAs
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The role of bromide in the formation and speciation of disinfection by-products (DBPs) during chlorination was investigated. The molar ratio of applied chlorine to bromide is an important factor in the formation and speciation of trihalomethanes (THMs) and halogenacetic acids (HAAs). A good relationship exists between the molar fractions of THMs and the bromide incorporation factor. The halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be determined based on probability theory. The formation of HAAs, and their respective concentrations, can also be estimated through use of the developed model.
- Chang,Lin,Chiang
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p. 1029 - 1034
(2007/10/03)
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- Transient puffs of trace organic emissions from a batch-fed waste propellant incinerator
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Emissions data have been obtained from a waste propellant incinerator. The incinerator is a dual fixed hearth, controlled air incinerator equipped with acid gas and particulate scrubbing. Puffing has been evident in this waste propellant incinerator by spikes in the CO concentration. Transient puffs of organics may travel down the combustion chambers and lead to stack emissions. The major conclusions from this study are that (1) transient puffs are formed due to the semi-batch feed nature of the combustion process (causing a local oxygen deficiency) and high water content of the desensitized propellant; (2) in batch-fed combustors, puffs can contribute to most of the organic emissions (which are relatively low) measured with US EPA sampling and analytical methods; (3) it is estimated that batch-fed combustion contributes up to 7-18 times more emissions than steady-state combustion will generate; (4) by applying dispersion analyses to determine the amount of oxygen deficiency in the flame zone, the combustion zone concentration of CO during batch-fed operation could be as high as 160,000 ppm, compared to a measured peak stack concentration of 1200 ppm CO; and (5) an organic sample is collected and averaged over at least a 2-h period that smooths out the transient peaks of organics emissions during batch-fed operation. For emissions that are associated with long-term potential health impacts, this is an appropriate sampling method. However, if a compound has a short-term potential health impact, it may be important to measure the time-resolved emissions of the compound.
- Hart, John R.
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p. 559 - 569
(2007/10/03)
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- Brominated-trihalomethane formation from phenolic derivatives as a model of humic materials by the reaction with hypochlorite and hypobromite ions
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Among the 21 phenolic derivatives tested for the model system of the disinfection process in the natural water containing humic acid, 2-hydroxytoluene and 2,6-dihydroxybenzoic acid produced high yields of CHBr3 under the co-existence of NaOCl and NaOBr. In the study of distribution of THMs produced, the amount of CHBr3 increased with the relative concentration of NaOCl added to NaOBr. These results were similar to the case of halogenation of the humic acid under the co-existence of NaOCl and NaOBr.
- Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
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p. 957 - 958
(2007/10/03)
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- Modelling the formation of brominated trihalomethanes in chlorinated drinking waters
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The chlorination of water containing bromide and natural organic matter (NOM) leads to the formation of brominated trihalomethanes (THMs). The extent of brominated THM formation depends, inter alia, on the bromide:chlorine concentration ratio ([Br-]:[chlorine]). A reaction scheme is proposed from which a simple kinetic model is developed that mathematically relates the extent of bromination, and the relative abundances of the four THMs, to the [Br-]:[chlorine] ratio. In the scheme, the trihalogenated precursors to THMs are formed by three steps each of which substitutes either bromine or chlorine into an activated carbon site in the NOM. This leads to six pairs of competing bromination:chlorination reactions, whose rate constant ratios (k(b):k(c)) have been estimated by using the model to fit THM data obtained from the chlorination of 17 waters from New Zealand. The individual k(b):k(c) ratios range from 4 to 15. From a plot of the ratio of total bromine to total chlorine present in the THMs as a function of the [Br-]:[chlorine] ratio, an apparent overall k(b):k(c) ratio of 9.1 is obtained. Using USEPA cancer potency factors, the model is used to predict the relative cancer risk associated with THMs as a function of the [Br-]:[chlorine] ratio. This risk increases steeply to a peak at a [Br-]:[chlorine] ratio of approximately 0.15, then gradually decreases to the value associated with bromoform alone. The risk associated with THMs may vary considerably through changes in the [Br-]:[chlorine] ratio as the result of natural variation in the [Br-], or through poor control of chlorine dosing.
- Nokes,Fenton,Randall
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p. 3557 - 3568
(2007/10/03)
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- Brominated trihalomethane formation in halogenation of humic acid in the coexistence of hypochlorite and hypobromite ions
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Brominated trihalomethanes (Br-THMs) such as CHCl2Br, CHClBr2, and CHBr3 are produced by the reaction of hypobromite with humic acid in the presence of hypochlorite. In the presence of excess NaOCl, addition of NaOBr enhanced the formation of Br-THMs but reduced the formation of CHCl3. The product distribution of THMs was affected by the ratio of [NaOBr]/[NaOCl] and was independent of pH and reaction time. In the presence of excess NaOBr, the yield of CHBr3 only increased linearly with the NaOCl concentration added. However, the other three THMs were hardly produced even though NaOCl concentration was increased up to 0.5 of the [NaOCl]/[NaOBr] molar ratio. Our results suggest that in the process of THM formation, hypochlorite ion reacts effectively with humic acid in the oxidation reaction and hypobromous acid plays a predominant role in the electrophilic substitution when both of hypohalites are present. Brominated trihalomethanes (Br-THMs) such as CHCl2Br, CHClBr2, and CHBr3 are produced by the reaction of hypobromite with humic acid in the presence of hypochlorite. In the presence of excess NaOCl, addition of NaOBr enhanced the formation of Br-THMs but reduced the formation of CHCl3. The product distribution of THMs was affected by the ratio of [NaOBr]/[NaOCl] and was independent of pH and reaction time. In the presence of excess NaOBr, the yield of CHBr3 only increased linearly with the NaOCl concentration added. However, the other three THMs were hardly-produced even though NaOCl concentration was increased up to 0.5 of the [NaOCl]/[NaOBr] molar ratio. Our results suggest that in the process of THM formation, hypochlorite ion reacts effectively with humic acid in the oxidation reaction and hypobromous acid plays a predominant role in the electrophilic substitution when both of hypohalites are present.
- Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
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p. 477 - 483
(2007/10/03)
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- Chemistry of the biosynthesis of halogenated methanes: C1-organohalogens as pre-industrial chemical stressors in the environment?
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We have chemical evidence that in the biosynthesis of the halomethanes C1H(4-n),X(n) (n = 1-4) three different pathways of biogenic formation have to be distinguished. The formation of methyl chloride, methyl bromide, and methyl iodide, respectively, has to be considered as a methylation of the respective halide ions. The dihalo- and trihalomethanes are formed via the haloform and/or via the sulfo-haloform reaction. The possible formation of tetrahalomethanes may involve a radical mechanism. Methionine methyl sulfonium chloride used as substrate in the incubation together with chloroperoxidase (CPO) and H2O2 gave high yields of monohalomethanes only. We were able to show that next to the CPO/H2O2 driven haloform reaction of carbonyl activated methyl groups also methyl-sulphur compounds - e.g. dimethylsulfoxide, dimethylsulfone, and the sulphur amino acid methionine - can act as precursors for the biosynthesis of di- and trihalogenated methanes. Moreover, there is some but not yet very conclusive evidence for an enzymatic production of tetrahalogenated methanes. In our experiments with chloroperoxidase involving amino acids and complex natural peptide based substrates, dihalogenated acetonitriles and several other volatile halogenated but yet unidentified compounds were formed. On the basis of these experiments we like to suggest that biosynthesis of halogenated nitriles occurs in general and therefore a natural atmospheric background should exist for halogenated acetonitriles and halogenated acetaldehydes, respectively.
- Urhahn, Thorsten,Ballschmiter, Karlheinz
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p. 1017 - 1032
(2007/10/03)
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- Kinetics of the R + Cl2 (R = CH2Cl, CHBrCl, CCl3 and CH3CCl2) reactions. An ab initio study of the transition states
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The kinetics of the reactions of CH2Cl, CHBrCl, CCl3 and CH3CCl2 radicals with molecular chlorine were investigated in a heatable tubular reactor coupled to a photoionization mass spectrometer. The reactions were studied under pseudo-first-order conditions. The radicals were photogenerated at 248 nm. The pressure-independent rate constants determined were fitted to the following Kooij and Arrhenius expressions (units in cm3 molecule-1 s-1): k-(CH2Cl) = 7.56 × 10-17(T)1.45 exp(-350 J mol-1/RT), k(CHBrCl) = 5.83 × 10-20(T)2.3 exp(-300 J mol-1/RT), k(CCl3) = (8.4 ± 2.9) × 10-13 exp[-(25 ± 9) kJ mol-1/RT] and k(CH3CCl2) = 1.10 × 10-26(T)4.3 exp(+15000 J mol-1/RT). The Arrhenius rate expression for the Cl + CCl4 reaction was determined to be k(Cl + CCl4) = (3.9 ± 3.2) × 10-13 exp[-(71 ± 9) kJ mol-1/RT] using the kinetics measured and the thermochemistry of the CCl3 radical. Errors for the Kooij expressions were estimated to be 25% overall, and for the Arrhenius expressions they were calculated to be 1σ + Student's t values. The transition states of the measured R + Cl2 and four other similar reactions were localized and fully optimized at the MP2/6-31G(d,p) level of theory by ab initio methods. The energetics of the reactions were considered by determining thermochemical and activation parameters of the reactions. The reactivity differences of the radicals studied were explained by a free-energy correlation using an electronegativity difference scale.
- Seetula, Jorma A.
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p. 3561 - 3567
(2007/10/03)
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- Facile halogen exchange reactions: Chloroform with bromoform and carbon tetrachloride with carbon tetrabromide
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Both of the title systems undergo rapid halogen exchange (half-life ca. 1-2 min) in N-methylpyrolidinone with catalytic sodium hydroxide at room temperature. Yet they differ markedly in response to added p-dinitrobenzene. The rate of the haloform exchange is unaffected, whereas the rate of the carbon tetrahalide exchange is severely retarded. The known base-induced halogen exchange reaction between chloroform and bromoform is shown not to proceed through a reversible carbene intermediate as claimed in the literature. It appears to be best described in terms of the so-called RARP mechanism (radical anion-radical pair). The mechanism proposed for the rapid exchange between carbon tetrachloride and carbon tetrabromide is initial electron transfer, halide ion loss, and ensuing radical chain scrambling of halogen atoms. The acronym RARC, standing for radical anion-radical chain, is proposed.
- Orvik, Jon A.
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p. 4933 - 4936
(2007/10/03)
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- Fluoride anion catalyzed halogen dance in polyhalomethanes
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Tetrabutylammonium fluoride catalyzes the exchange of halogens between tetrahalomethanes.The presence of small amounts of haloform is suspected to be a necessary co-catalyst.Key Words: tetrabutyl ammonium fluoride; tetrahalomethanes; halogen exchange in.
- Sasson, Y.,Kitson, F.,Webster, O, W.
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p. 599 - 600
(2007/10/02)
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- Kinetics of the Reactions of Halogenated Methyl Radicals with Molecular Bromine
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The kinetics of seven reactions of halogenated methyl radicals (CH2Cl, CHCl2, CFCl2, CF2Cl, CF3, CH2Br, and CH2I) with molecular bromine were studied by using a heatable tubular reactor coupled to a photoionization mass spectrometer.Rate constants were measured as a function of temperature, typically between 296 and 532 K.Arrhenius activation energies were found to be small negative values (typically -2 kJ mol-1) for all reactions studied with the exception of that of the CF3 + Br2 reaction (whose activation energy is positive, but which could not determined accurately).The pattern of reactivity among 11 reactions of substituted methyl radicals with Br2 (which includes the 7 reactions studied here and 4 C(H)x(CH3)3-x + Br2 reactions (x = 0-3) studied earlier) has been accounted for by the inductive effect of the substituent atoms or groups.The sum of the Pauling electronegativities of these substituents provides a useful measure of their total inductive effect on the reaction rate constant.
- Timonen, R. S.,Seetula, J. A.,Niiranen, J.,Gutman, D.
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p. 4009 - 4014
(2007/10/02)
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- Specific Catalyst Effects on Halogen-Exchange Processes with Mixed Dihalogenocarbenes
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An improved preparation of chlorodiiodomethane and dibromochloromethane by phase-transfer catalysis is described.Bromochlorocarbene is generated from HCBr2Cl highly selectively (>=97percent) only if tetramethylammonium chloride, dibenzo-18-crown-6, its 3,3',5,5'-tetra-tert-butyl derivative, or 3',5'-di-tert-butylbenzo-15-crown-5 are catalysts.Other investigated catalysts promote extensive halide exchange whereby olefin adducts of dibromo- and dichlorocarbene are formed additionally.
- Dehmlow, Eckehard V.,Stuetten, Joerg
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p. 187 - 190
(2007/10/02)
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- Absolute Rate Constants for Bromine Abstraction from N-Bromoimides and Br2 by Alkyl Radicals
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Imidyl radicals react with cyclopropanes solely via hydrogen abstraction.In the case of methylcyclopropane, the major product (cyclopropylcarbinyl bromide) is derived from abstraction of hydrogen from the methyl group.The resultant cyclopropylcarbinyl radical is partioned between two pathways: (1) abstraction of Br from N-bromoimide and (2) rearrangement to the allylcarbinyl radical (eventually yielding 4-bromo-1-butene).Since the absolute rate of the rearrangement is known, an absolute rate constant for the abstraction of Br from N-bromoimides by alkyl radicals can be derived (CH2Cl2 solvent, 15 deg C), k ca. (1.3-1.6)1xE10 M-1s-1.Reactions carried out in the presence of Br2 provide a third pathway for scavenging of the cyclopropylcarbinyl radical, providing kBr2=2.2x1E10 M-1s-1.Thus, trapping of primary R. by either N-bromoimides or Br2 occurs at rates that are diffusion-controlled.
- Tanko, James M.,Skell, Philip S.,Seshadri, Sri
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p. 3221 - 3225
(2007/10/02)
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- Electron Transfer Reactions in Organic Chemistry. XIV. The Reactivities of Some Polyhaloalkanes toward the Outer-Sphere Electron Transfer Reductants Co(II)sepulchrate2+ and Co(II)W12O407-
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Rates were measured for the title reactions in CH3CN/H2O buffered at pH ca.7 at 20 or 50 deg C.The following order of reactivity toward Co(II)W12O407- was found: CBr4 > (CBrCl2)2 > CBr2Cl2 > C2Cl6 > CBrCl3 > CF3CHClBr > CHBr3 > CCl4.Only CBr4, (CBrCl2)2, CBr2Cl2 and CBrCl3 gave measurable rates of reaction with Co(II)sepulchrate2+, and with the same order of reactivity as above.Four these four substrates, a plot of log kET2+ had a slope close to 1.Qualitative product studies for the reactions with Co(II)W12O407- showed that the polyhalomethanes generally reacted by losing their heaviest halogen, while polyhaloethanes formed ethylenes by losing their havies halogen on each carbon atom.For some of the reactions, the intermediate radical formed in the first step could be trapped by N-t-butyl-α-phenylnitrone.The resulting spin adducts were detected by ESR spectroscopy.It is agrued that the rate constant difference between CBr4 and CBrCl3 supports the notion of a very short-lived intermediate anion radical.
- Eberson, Lennart,Ekstroem, Mikael
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p. 113 - 121
(2007/10/02)
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- Fe3O4-Catalyzed Halogen-Exchange Reactions of Polyhalomethanes
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Triiron tetraoxide pretreated by polyhalomethane was shown to catalyze the halogen-exchange reaction of polyhalomethanes CHlBrmCln (l=1 or 2).The exchange proceeds consecutively giving, for example, CHBrCl2, CHBr2Cl, and C
- Nakada, Masahiro,Tokumoto, Sei-ichi,Hirota, Minoru
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p. 3979 - 3984
(2007/10/02)
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- REACTIONS OF BrCl WITH ALKYL RADICALS.
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It is demonstrated that photohalogenation of low reactivity substrates with BrCl occurs mainly with Cl. selectivity.With tertiary or benzylic hydrogens in the substrate, mainly Br. selectivity is observed.These observations are rationalized, taking into account the relative concentrations of halogen atoms and their respective rates of hydrogen abstractions.The resultant radicals react with BrCl to make (RBr/RCl) in ratios between 1 and 15.
- Skell, P. S.,Baxter, H. N.,Tanko, J. M.
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p. 5181 - 5184
(2007/10/02)
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- Ground- and Excited-State Succinimidyl Radicals in Chain Reactions: A Reexamination
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The succinimidyl radical chemistry reported earlier and previously attributed to the ? state is reproduced, leaving unsettled only its assignment to the ? and ? state.This chemistry, observed in the presence of small amounts of alkenes which scavenge bromine, includes the following: (1) additions to alkenes, (2) additions to arenes, (3) Cl-like substitution selectivities, and (4) ring-openings.The chemistry previously reported under the title "?" is neither as simple nor conclusive as thought earlier.As reported earlier, ring-opening is suppressed by inclusion of bromine, benzene, bromotrichloromethane, or larger amounts of alkenes.These observations indicate the presence of a different chain carrier, formerly labeled as S?.We show now that the S? explanation was not correct with addends benzene, bromotrichloromethane, and olefins, and we identify the specific competitive processes.Reactions in the presence of bromine still show evidence for a third hydrogen abstractor besides an imidyl radical and a bromine atom.At this time there is no unambiguous identification of this third chain intermediate.
- Skell, Philip, S.,Luening, Ulrich,McBain, Douglas S.,Tanko, James M.
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p. 121 - 127
(2007/10/02)
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- The Walling, El-Taliawi, and Zhao "Carnonyl Effect" in Radical Brominations Is an Example of HBr Reversal. It Is Not Relevant to ? and ? Radical Chemistry.
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Walling, El-Taliawi, and Zhao claim that our "S? chemistry" is reproduced in photobrominations employing Br2 in the presence of carbonyl compounds (no NBS).Photobromination of alkanes by N-bromosuccinimide (NBS) shows selectivities that vary, but which show limiting values for significant ranges of rection conditions.We have attributed these different limiting values to three reaction paths which differ in involving either Br., S?, or S? as the intermediate hydrogen-abstracting radical.Walling, El-Taliawi, and Zhao (WEZ) have reported selectivities they belive are attributable to a carbonyl-bromine intermediate rather than our S?.Evidence is now presented to show that the WEZ results are due to HBr in varying amounts with or without carbonyl compounds present.This represents a fourth type of selectivity and one that is sensitive to HBr concentrations and probably arises in their systems from the following reaction: There is no carbonyl effect.This fourth type had been deliberately excluded from our work, so that reactions involving HBr reversal are not relevant to our published work on succinimidyl chemistry.Thus, the selectivities (per H basis) for the neopentane/methylene chloride competitions stand without modification, as published earlier: 0.067, 1.0 and 17 for B., S?, and S?, respectively.
- Skell, P. S.
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p. 1838 - 1840
(2007/10/02)
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- Radical Chain Carriers in N-Bromosuccinimide Brominations
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Relative reactivities per hydrogen (r's) for neopentane-CH2Cl2 have been redetermined for photobromination by Br2, r = 0.03-0.4, NBS + Br2, r = 1-2.5, and NBS + 1,1-dichloroethylene (DCE) as a Br. trap, r > 20.In the last case β-bromopropionyl isocyanate (BPI) is the major product.In Br2 reactions r's vary with experimental conditions and are increased significantly by a number of carbonyl and succinimide derivatives.BPI is also a major product in the brominaton of CHCl3 in the presence of DCE and in the UV photolysis of NBS in CD2Cl2 even in the presence of Br2.For CH2Cl2-CD2Cl2 mixtures, kH/kD ca. 10 for both NBS-Br2 and NBS-DCE systems.The kinetics of decomposition of NBS in CH2Cl2 in the presence of Br2, initiated by UV light, azobis(isobutyronitrile) and benzoyl peroxide are zero order in NBS, with k for attack of the chain-carrying radical on CH2Cl2 estimated as 55 at 50 deg C.In the presence of DCE, benzoyl peroxide initiated reactions in CH2Cl2 are also zero order, with rates corresponding to a rate constant for ring opening kd ca. 1660.Addition of cyclohexane produces an unexpected increase in rate corresponding to kd ca. 1.5*104, and k for reacton of the succinimide radical with cyclohexane ca. 104.If these rate constants are valid, they require a radical lifetime of ca. 10-4 s, and this and their low value appear inconsistent with a high-energy excited state of the succinimide radical.It is proposed that the chain carrier in the NBS-Br2 system is a reaction product of NBS and a bromine atom, for which some possible structures are suggested.
- Walling, Cheves,El-Taliawi, Gamil M.,Zhao, Chengxue
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p. 5119 - 5124
(2007/10/02)
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- SELECTIVITIES OF pi - AND sigma -SUCCINIMIDYL RADICALS IN SUBSTITUTION AND ADDITION REACTIONS. APPENDIX: RESPONSE TO WALLING, EL-TALIAWI, AND ZHAO.
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A new method for studies of pi -succinimidyl (S// pi ) radicals is described, one that makes possible the study of reactions of this radical with a variety of substrates not accessible by the use of Br//2-NBS. NBS systems containing BrCCl//3 at mole fractions greater than 0. 3 show all the characteristics associated with S// pi behavior, and they function in the presence of olefins which serve as Br//2 scavengers. If CCl//4 is substituted for BrCCl//3, the system is clearly S// sigma . The S// pi behavior is contrasted with S// sigma and Br multiplied by (times) reactivities for H abstractions from a variety of substrates and for additions to tert-butylethylene, isobutylene, and 1,3-butadiene. In early-transition-state systems, for H transfer, the strength of the bond being broken and the strength of the bond being made are not the major factors in determining reactivities. The behavior in late-transition-state systems is influenced by both bond strengths. The S// pi radical shows intermediate behavior. These conclusions are supported by primary deuterium isotope effects for methylene chloride and chlororoform. The Appendix addresses a number of questions raised by the preliminary study of NBS reactions by Walling et al.
- Skell,Tlumak,Seshadri
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p. 5125 - 5131
(2007/10/02)
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- Reactions of a Graded Set of Radicals with N-Bromosuccinimide; Two Transition States
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The reactions of N-bromosuccinimide with a series of radicals have been studied.These reactions fall into two categories, the more reactive radicals producing ?-succinimidyl and the less reactive radicals producing ?-succinimidyl.The threshold for the changeover from one reaction domain to the other occurs with radicals less reactive than secondary alkyls.These results are interpreted with two transition states, an in-line transition state for the more reactive radicals and an out-of-plane transition state for the less reactive radicals. An upper limit of 18 kcal/mol is established for the enthalpy difference, HS? - HS?.Two new methods for generating S? radicals are indicated.
- Tlumak, Robert L.,Skell Philip S.
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p. 7267 - 7274
(2007/10/02)
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- Catalytic Halide Exchange in Hydrocarbons Promoted by Aluminas Coated with Phosphonium Salts
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Passing a mixture of two different alkyl halides, in the gas phase, through a column filled with alumina and a phosphonium salt, gives halide-exchange products which are collected at the outlet by condensation; the process is catalytic and allows transformations to be carried out in a continuous flow process.
- Angeletti, Enrico,Tundo, Pietro,Venturello, Paolo
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p. 1127 - 1128
(2007/10/02)
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